Three-Dimensional Hückel Theory for closo-Carboranes

We have recently developed a 3-dimensional Hückel method for cluster compounds. The method uses a set of approximations for Coulomb, resonance, and overlap integrals very similar to those employed in the familiar 2-dimensional Hückel theory for the pi electrons of planar conjugated hydrocarbons. The method can be adapted to heteroatomic clusters by introducing heteroatomic Coulomb integrals, alpha(Y) = alpha(X) + hbeta, whereh is a parameter for heteroatom Y. In this paper, we use the 3-dimensional Hückel method to study the properties of the closo-carboranes, C(2)B(n)()(-)(2)H(n)(). We calibrate the method by choosing a value of the heteroatomic parameter h that distinguishes positional isomers by energy and gives them relative energies in rough agreement with those established by observation and ab initio calculations. We obtain modest improvement in matching ab initio relative energies of isomers by means of a three-parameter, first-order perturbation treatment. We use the calibrated method to evaluate various mechanisms proposed for the isomerizations of C(2)B(4)H(6), C(2)B(5)H(7), and C(2)B(6)H(8), all of which have been observed to undergo intramolecular isomerizations. Rearrangements of C(2)B(6)H(8) have been satisfactorily explained by a single-DSD (diamond-square-diamond) process. Those for C(2)B(5)H(7) require at least two DSD processes, concerted, consecutive, or overlapping. Several different mechanisms have been proposed for the rearrangement of C(2)B(4)H(6). In evaluating intermediate and transition state structures, the 3-dimensional Hückel method gives higher energies to those structures with a larger number of nontriangular faces, a plausible conclusion except that occasionally it is wrong. In comparison with ab initio results, the 3-dimensional Hückel method fails to give low energies for classical structures.     

Theory of Triangular-wave Oscillovoltametry -Single Electrode Reaction

The theory of single electrode reaction in triangular-wave a.c. oscillovoltametry is presented. Theoretical equation for E-t curve is derived, and transition time, incision potential and incision height are described quantitatively.some important results are expresed below:     

Chemical Frequencymetry——Theory and Application

A new theory named "Chemical frequencymetry" is proposed. It is based on chemical reactions followed by piezoelectric monitoring. The frequency shift caused by the chemical reaction is related to the fundamental frequency (f) and overtone order (h) of the crystal, the formula weight (m) and diffusion coefficient (D) of the active chemical species, the diffusion layer thickness (δ), the response time(t), the concentration of the determinant (C_A) and the stoichiometric factor of the chemical reaction (k) according to the formulaThe technique has been applied to the determination of analgin as an example of its application.     

Polymer Holography – New Theory of Image Growth

Summary: The image forming process in photopolymer holographic film has been studied thoroughly. Many grow-curves, i.e. the curves describing the time dependence of the image grow, have been obtained by the special equipment (described in 1 ) under varying conditions. The varying concerns both the changes in film composition and exposition. The S-type form of the measured grow curves bring out some problem in interpreting them in the framework of the usual diffusion theories of photopolymer image growth. To overcome the problem we add the idea that polymer loses its mobility as it grows to the usual only diffusion theories and put down the more general immobilization-diffusion theory. 2     

Fluctuating Hydrodynamics and Debye-Hückel-Onsager Theory for Electrolytes

We apply fluctuating hydrodynamics to strong electrolyte mixtures to compute the concentration corrections for chemical potential, diffusivity, and conductivity. We show these corrections to be in agreement with the limiting laws of Debye, Hückel, and Onsager. We compute explicit corrections for a symmetric ternary mixture and find that the co-ion Maxwell-Stefan diffusion coefficients can be negative, in agreement with experimental findings.     

Theory comparison and choice in chemistry, 1766–1791

This is the second of a pair of papers, of which the first showed how each of the main late phlogistic theories effectively reached impasses due to internal problems or included features which made them unacceptable even to other phlogistians. This paper deals with theory comparison and theory change. It gives an unprecedentedly detailed comparison between the available theories in 1790–1791, and shows that this was overwhelmingly in favour of the new chemistry. This time period correlates well with many chemists changing to the new theory. There was a plurality of views held by individuals and there was freedom of individual choice concerning theories, yet there was also a widespread and rational change to the new chemistry.     

Broadband Vibrational Cooling of Cold Cesium Molecules： Theory and Experiments

The use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample of cold molecules, initially distributed over several vibrational levels, has thus been transfered into a single selected vibrational level of the singlet X^1∑g ground electronic state. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. In this paper we briefly report the main experimental results and then address, in a detailed way by computer simulations, the perspectives for a ＂complete＂ cooling of the molecules, including also the rotational degree of freedom. Since the pumping process strongly depends on the relative shape of the ground and excited potential curves, ro-vibrational cooling through different excited states is theoretically compared.     

Calculation of Visible Absorption Maxima of Phthalocyanine Compounds by Quantum Theory

Based on HYPERCHEM, the structures of five phthalocyanie compounds wereo ptimized with PM3 and their visible absorption maxima were calculated with ZINDO/S methodby selecting appropriate π-π overlap weighting factor (OWFπ-π), the agreement with experiment was excellent. The relationship between OWFπ-π and molecular structure parameters was obtained by the method of stepwise regression and was explained in terms of quantum theory. OWFπ-π=0.58126 0.04562ANC 1 0.03839X.Where, ANC 1 and X are the symbols of average net charges on coordinated bonded nitrogens and electronegativity of central atom, respectively.     

Adsorption Study of Methane on Activated Meso-carbon Microbeads by Density Functional Theory

A combined method of density functional theory (DFT) and statistics integral equation (SIE) for the determination of the pore size distribution (PSD) is developed based on the experimental adsorption data of nitrogen on activated mesocarbon microbead (AMCMB) at 77K. The pores of AMCMB are described as slit-shaped with PSD.Based on the PSD, methane adsorption and phase behavior are studied by the DFT method. Both nitrogen and methane molecules are modeled as Lennard-Jones spherical molecules, and the well-known Steele‘s 10-4-3 potential is used to represent the interaction between the fluid molecule and the solid wall. In order to test the combined method and the PSD model, the Intelligent Gravimetric Analyzer (IGA-003) was used to measure the adsorption of methane on the AMCMB. The DFT results are in good agreement with the experimental data. Based on these facts,we predict the adsorption amount of methane, which can reach 32.3ω at 299K and 4 MPa. The results indicate that the AMCMBs are a good candidate for adsorptive storage of methane and natural gas. In addition, the capillary condensation and hysteresis phenomenon of methane are also observed at 74.05K.     

Nonequilibrium Solvent Free Energy Curve from Molecular Theory in Electron Transfer Reaction

l.IntroductionEleCtrontransfer(ET)reactionisamongthemostfundaInentalofcheIIilstryandbiochendsny.Thetwrtanroleofevaluationofthes0lventfreeenergyandthercorganhaionenergyaninETprocesshasalwaysbeenreeogfordbyanextensiveliteratureindilsfield[1-2].HeneehowtochooseasuitablesolventreactioncoordinaeandconsequentlyconstructtheassociatedfreeenergyfimtionbecomesthCpriInnysteP,andalsotheaPplicabilityoftheenergygaPlaw.Manyrecentstudiesarefocusedonthesolventpolarizaionandsolventdyndcalbehaviorandmpmeeh…     

ChemInform Abstract: Is CrF6 Octahedral? Theory Suggests Not!

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Crystal Structure and Density Functional Theory Studies of （p-Methoxyphenyl） Thiosemicarbazide

1 INTRODUCTION Recently, the discoveries of antitumor effects ofinorganic complexes, especially of metal complexes,and their applications for curing cancer diseaseshave received increasing attention[1]. As a ligandwith potential S and N donors, thiosem…     

Density Functional Theory Study on La Complex with Schiff-base as Building Block

1 INTRODUCTION Recently, there has been a growing interest[1~5] inlanthanon complexes because of their abundant stru-ctural characters and important biologic activities.The complexes are extensively used as coordinationand stabilization agents[6, 7] for the measures of me-tallic ions, antibacterial and anticancer drugs[8], cata-lysts for vitamin B6 in amination and oxidation re-actions[9], biological models of N2, O2 carriers andaminophenol asymmertry synthesis and preparationof nonprote…     

Theory of photon statistics in single-molecule Förster resonance energy transfer

We present the theory for the distribution of the number of donor and acceptor photons detected in a time bin and the corresponding energy-transfer efficiency distribution obtained from single-molecule Forster resonance energy-transfer measurements. Photon counts from both immobilized and freely diffusing molecules are considered. Our starting point is the joint distribution for the donor and acceptor photons for a system described by an arbitrary kinetic scheme. This is simplified by exploiting the time scale separation between fast fluorescent transitions and slow processes which include conformational dynamics, intersystem conversion to a dark state, and translational diffusion in and out of the laser spot. The fast fluorescent transitions result in a Poisson distribution of the number of photons which is then averaged over slow fluctuations of the local transfer efficiency and the total number of photons. The contribution of various processes to the distribution and the variance of the energy-transfer efficiency are analyzed.     

Generalized two-dimensional correlation spectroscopy——Theory and applications in analytical field

After correlation analysis for general spectro- scopy, two-dimensional (2-D) correlation spectroscopy is obtained by extracting the information contained in the spectra in two dimensions, which is the function of two dependent spectral variables. 2-D correlation spectroscopy is initially regarded as an analytical data treatment method in the study of molecular interaction by using sinusoidal infrared sign[1]. In 1993, it was extended to generalized 2-D correlation spectroscopy, which used mo…     

Filtration in Nonuniform Capillary–Porous Media: Equations of the Statistical Theory

Relationships between the statistical distribution of the filtration coefficient in a nonuniform capillary–porous medium and its total value for a filter layer are obtained. A closed set of equations where higher-order correlation moments of statistical fields serve as transferable entities is derived. The approach developed in this study makes it possible to study detailed laws of filtration in a nonuniform capillary–porous medium using the data on the filtration coefficient statistics, which is determined by the structure of the porous space.